26266: What is the ruling on neglecting the Sunan al-Fitrah, and does that have any effect on tahaarah (purity)?

I have noted that some worshippers let their nails grow long and they are filled with dirt. Is this befitting for a Muslim? Is their wudoo’ valid? Is there a specified time limit for cutting the nails, or for doing other things that are Sunan al-Fitrah (specific sunnahs connected to the natural disposition of man)?

Praise be to Allaah.

The nails must be cut
within forty days (of the last cutting), because the Messenger of Allaah
(peace and blessings of Allaah be upon him) specified a time limit
within which people should cut their nails, shave their pubic hair, pluck
their armpit hair and trim their moustaches, and not leave it for more than
forty days. This was proven from the Messenger of Allaah (peace and
blessings of Allaah be upon him). Anas (may Allaah be pleased with him), who
was the servant of the Messenger of Allaah (peace and blessings of
Allaah be upon him) said: “He set a time for us to trim our moustaches, cut
our nails, pluck our armpit hair and shave our pubic hair; we were not to
leave that for more than forty days.” Narrated by Imaam Muslim in
al-Saheeh (258). It was also narrated by Imaam Ahmad (11823) and by
al-Nasaa’i (14) and a group with the wording: “The Messenger of Allaah
(peace and blessings of Allaah be upon him) set a time limit for us, we were not to neglect our nails and moustaches, and shaving the pubic hair and plucking the armpit hair beyond forty days.” Both men and women must pay attention to this matter and not leave the nails, moustache, pubic hair or armpit hair for more than forty days. Wudoo’ is valid and is not affected by whatever dirt is under the fingernails, because it is a small amount and may be forgiven.